1. Field of the Invention
The present invention relates to a process for hydrolyzing pyrodextrin with alpha-amylase derived from Bacillus licheniformis to prepare a pyrodextrin hydrolyzate.
2. Description of the Prior Art
U.S. Pat. No. 2,965,520 discloses a process for hydrolyzing (liquefying) starches with alpha-amylase, i.e., a process comprising hydrolyzing a starch slurry with an acid, adjusting the resulting hydrolyzate to a pH of 4 to 10, and adding alphaamylase (not comprising the amylase produced from B. licheniformis) for further hydrolysis to prepare a product with greater stability.
U.S. Pat. No. 3,249,512 discloses a process wherein a suspension of crude starch is hydrolyzed with alpha-amylase free from protease (and not comprising the amylase produced from B. licheniformis) at a pH of 6.5 to 7.5 and subsequently heated to 99.degree. C. to inactivate the alpha-amylase and to obtain a hydrolyzate of improved taste.
U.S. Pat. No. 3,378,462 discloses a process comprising adding a calcium salt and sodium salt to a starch slurry, adding bacterial alpha-amylase (not comprising the amylase produced from B. licheniformis) to the suspension at a pH of 5.5 to 7.7, and heating the mixture at 77.degree. to 93.degree. C. for hydrolysis to obtain a hydrolyzate of high DE.
U.S. Pat. Nos. 3,695,933, No. 3,756,853 and No. 3,756,919 disclose a process wherein a starch slurry having a concentration of up to 50% is hydrolyzed with bacterial alpha-amylase (not comprising the amylase produced from B. licheniformis) at a pH of 6.5 to 8.0 at 80.degree. to 95.degree. C., and a two-step liquefaction process using amylase which comprises this process and wherein the hydrolyzate obtained by the process is heated to 150.degree. C., then cooled to 80.degree. to 90.degree. C. and hydrolyzed again with the addition of bacterial alpha-amylase. The two-step process, which is similar to the process of U.S. Pat. No. 2,965,520, is adapted to achieve an improved filtration rate.
U.S. Pat. No. 3,849,194 discloses a process for preparing a starch hydrolyzate 5 to 20 in DE and non-hazing by adding bacterial alpha-amylase (not comprising the amylase produced from B. licheniformis) to a waxy starch slurry at a pH of 6 to 8 to effect hydrolysis approximately to DE 5 at a temperature of at least 85.degree. C., and subsequently lowering the temperature below 80.degree. C. without heat-treatment to effect further hydrolysis.
U.S. Pat. No. 3,853,706 discloses a process comprising adding bacterial alpha-amylase (not comprising the amylase produced from B. licheniformis) to a slurry of nonwaxy starch having a concentration of up to 40%, hydrolyzing the suspension to DE 2 to 15 at a temperature of up to 95.degree. C., heating the hydrolyzate above 95.degree. C., then cooling the hydrolyzate to below 85.degree. C., and further hydrolyzing the hydrolyzate to DE 5 to 20 with addition of bacterial alpha-amylase to obtain a nonhazing syrup.
U.S. Pat. No. 3,910,820 discloses a process wherein a slurry of crude starch is heated at 50 to 60.degree. C. for 1 to 5 hours as a pretreatment before the addition of alpha-amylase for hydrolysis, then hydrolyzed with alpha-amylase (not comprising the amylase produced from B. licheniformis) at 80 to 105.degree. C., subsequently cooled to 70.degree. to 85.degree. C. without heat-treatment, and thereafter hydrolyzed with an additional amount of alpha-amylase to obtain a hydrolyzate which is easy to refine.
U.S. Pat. No. 3,912,590 discloses a short time hydrolysis process wherein a stach slurry having a concentration of at least 25% is hydrolyzed at 100.degree. to 115.degree. C. for 1 to 60 minutes with alpha-amylase produced from B. licheniformis, followed by cooling to 80.degree. to 100.degree. C. and hydrolyzed to at least DE 12 without heat-treatment and without using an additional amount of alpha-amylase.
U.S. Pat. No. 4,298,400 discloses a process wherein a slurry of nonwaxy starch is hydrolyzed with alpha-amylase produced from Bacillus subtilis or Bacillus mesentericus at a pH of 7.5 to 8 at 90.degree. to 92.degree. C. to below DE 15, followed by heating to 150.degree. C., then cooling to 80.degree. to 85.degree. C. and thereafter hydrolyzed to DE 5 to 20 with an additional amount of alpha-amylase to obtain a non-hazing syrup.
U.S. Pat. No. 4,410,368 discloses a process comprising of adding a carbonate (pH buffer) to a starch slurry having a concentration of 15 to 30% to adjust the suspension to a pH of 6 to 8, adding heat-resistant bacterial alpha-amylase (produced from B. licheniformis) to the slurry, heating the slurry to 100.degree. to 110.degree. C. over a period of 5 to 15 minutes to effect hydrolysis, then heating the hydrolyzate at 140.degree. to 150.degree. C. for 15 to 40 minutes, subsequently cooling the hydrolyzate to 95.degree. to 100.degree. C., hydrolyzing the hydrolyzate with an additional amount of alpha-amylase for 5 to 30 minutes approximately to DE 2, and further adding beta-amylase to the resulting hydrolyzate for saccharification to obtain a hydrolyzate suitable for preparing maltose.
U.S. Pat. Nos. 4,684,410, No. 4,689,088, No. 4,699,669 and No. 4,699,670 disclose a process comprising hydrolyzing a starch slurry with an acid or enzyme up to DE 3, adding bacterial alpha-amylase to the hydrolyzate at a pH of 6.5 to 8 and effecting hydrolysis at 95.degree. to 100.degree. C. to obtain a hydrolyzate which can be filtered with an improved rate.
U.S. Pat. No. 4,933,279 discloses a process comprising adding a mixture of bacterial alpha-amylases produced from B. licheniformis and Bacillus stearothermophilus to a slurry of starch or starchy grains at a pH of 5.5 to 6.2, hydrolyzing the slurry at 100.degree. to 115.degree. C. for 1 to 60 minutes, and cooling the hydrolyzate to 90.degree. to 100.degree. C. without heat treatment, followed by hydrolysis for 30 to 180 minutes to obtain a hydrolyzate with elimination of any problem of sediment.
With respect to the enzymatic hydrolysis of pyrodextrin, nothing has been reported except that B. Brimhall, Ind. Eng. Chem., 36, 72(1944) states that when British gum prepared by heating starch without adding any acid thereto is hydrolyzed with alpha-amylase (not comprising the amylase produced from B. licheniformis), the limit of decomposition is 3.5% calculated as maltose, i.e., about 7.4 calculated as DE.
However, these processes are hydrolysis (liqueiaction) processes for starch, crude starch or pyrodextrin prepared without the addition of acid, with any of these processes encountering difficulties when used for hydrolyzing pyrodextrin of the type mentioned, and are not suited to practice for this purpose. Stated more specifically, when water is added to starch, particles of starch become suspended in water to form a starch slurry without dissolving in water, whereas if water is added to pyrodextrin, pyrodextrin dissolves in water to make a highly viscous solution. Accordingly, when pyrodextrin is dissolved in water to a usual hydrolyzing concentration of 30 to 45% in the first step for the enzymatic hydrolysis of pyrodextrin, the solution becomes highly viscous and difficult to prepare, while the solution, if prepared, is difficult to stir and to transport by pumping for transfer to the subsequent process. Additionally, the acid used for the preparation of pyrodextrin reacts with the protein, oil and fat present in starch during heating to form impurities, which are extremely difficult to remove for purification since some of them are combined with starch. These impurities remain even after the hydrolyzate has been decolorized, filtered and desalted with ion exchange resin, rendering the product non-transparent and permitting the product to contain many colored substances. In the case where the product is used for foods, pharmaceuticals and industrial applications which are the main uses of pyrodextrin, such impurities are prone to react with various other components, and are likely to produce precipitates during or after the production of food or the like, hence a serious drawback. Further the hydrolysis process wherein an acid is used has the defect that the characteristic decomposition mechanism of the acid is liable to impair the inherent properties of pyrodextrin.